Effusion cooling of the combustor walls of a turbine engine, as taught in EPC Application No. 0-486-226-AP, published May 20, 1992, has heretofore been employed to maintain a desired wall temperature in the combustor. Effusion cooling may be defined as a pattern of small, closely spaced holes serving to direct a flow of cooling air onto the walls of a gas turbine combustor. The cooling holes are generally 0.15 to 0.35 inches in diameter, and are angled relative to the combustor wall so that the hole centerline forms an angle of approximately 20 degrees with a tangent to the hot gas side of the combustor wall surface. Individual hole shape is generally cylindrical, with minor deviations due to manufacturing method i.e. edge rounding, tapers, out-of-round or oblong, etc.
Such known effusion cooling systems exhibit a two-fold cooling effect, namely (a) convectively cooling the combustor wall as the air passes through the holes, and (b) providing a continuously replenished surface cooling film. Orientation of the holes with respect to the direction of bulk gas flow in the combustor has heretofore been undisciplined. Thus, while such known effusion cooling systems result in greatly enhanced combustor wall cooling compared with typical louvered film cooled designs, the combination of effusion cooling with purging of near-injector recirculation, as well as cooling film flow geometry over the combustor liner so as to augment fuel distribution and start performance has not been addressed.
More specifically, known effusion cooling systems do not contemplate or solve problems relating to radial outflow combustor geometry. The effect of effusion cooling hole groupings, patterns and orientations on control of local combustor aerodynamics must be considered as well as cooling effectiveness.
Gas turbine combustor liners have heretofore employed various forms of louvers or thumbnail-style surface film distributors that are circumferentially distributed in spaced relation at discrete intervals. Also, it is known to provide specific aerodynamic treatment in the form of air guides adjacent fuel slingers to purge local, fuel rich, fuel/air mixture recirculation. Such methods generally attenuate the efficiency of film cooling air to control local over-temperature conditions of the combustor walls with resultant erosion and reduced durability. Moreover, known techniques of purging the near-injector area of the combustor often result in build-up of carbon or localized flame holding, interfering with fuel injection and reducing starting performance and durability.